The invention concerns a high voltage vacuum feed through for an electron tube, in particular, for a solid anode X-ray tube, comprising                an insulating body of ceramic material, wherein the insulating body has a continuous hollow space,        and an anode, wherein a rear end of the anode is arranged in the hollow space of the insulating body and seals the hollow space in a vacuum-tight fashion.        
A vacuum feed through of this type is disclosed e.g. in DE 10 2009 017 924 A1.
X-ray radiation is used in various ways in instrumental analysis or also for producing image recordings of human and animal patients in medicine. X-ray radiation is typically generated in an X-ray tube through emission of electrons from an electrically heated electron emitter and acceleration of the electrons in the electrical field to a so-called target, from which characteristic X-ray radiation is emitted. The target material differs in dependence on the application. The electron emitter is part of a cathode and the target is part of an anode.
In order to be able to sufficiently accelerate the electrons towards the target, the space between the cathode and the anode must be evacuated and a high voltage (typically some kilovolts) must also be applied between the cathode and the anode. In most cases, a high voltage is applied to the anode, which requires a corresponding vacuum-tight feed through. A high voltage vacuum feed through usually comprises a ceramic body as electric insulator with a central opening into which a high voltage lead and an electrode are inserted in a vacuum-tight fashion, cf. EP 1 537 594 B1.
In one embodiment of DE 10 2009 017 924 A1, the anode is produced of copper and is soldered into a tubular ceramic insulating body of aluminium nitride in a vacuum-tight fashion.
However, copper and ceramic materials such as aluminium nitride have quite different thermal expansion coefficients such that, during soldering or also due to load (and heating) during operation, large mechanical stress may be generated which can result in that the soldering joints leak. The X-ray tube is then useless.
DE 10 2009 924 A1 proposes to form elastic claws on the outside of the anode. These claws can elastically absorb the mechanical stress and also adjust the heat flow. Alternatively, the anode could terminate in a soft-annealed hollow cylindrical section, where only small mechanical stress is generated.
The production of elastic claws on the anode is very complex and vacuum-tight soldering to the ceramic insulating body is much more complicated in comparison with an anode having a smooth outer wall. An anode with a hollow-cylindrical section is only suited for relatively small heat flows, i.e. X-ray tubes with a comparatively small power. Another point is that the hollow-cylindrical section may easily become deformed during installation, which again aggravates vacuum-tight soldering.
The relatively complex process of installing an anode into a ceramic insulating body moreover results in comparatively long delivery periods in case it is not intended to stock finished vacuum feed throughs for any target type. In accordance with prior art, it is hardly possible to change the target at the front end of the anode after installation of an anode into the insulating body.
It is the underlying purpose of the present invention to provide a high voltage vacuum feed through which is easy to produce, can be designed to be reliably vacuum-tight and also remains reliably vacuum-tight during operation, in particular, wherein the high voltage vacuum feed through can also be easily equipped with different target materials.